In general it is always better to date a properly identified single entity (such as a cereal grain or an identified bone) rather than a mixture of unidentified organic remains.Common materials for radiocarbon dating are: The radiocarbon formed in the upper atmosphere is mostly in the form of carbon dioxide. Because the carbon present in a plant comes from the atmosphere in this way, the radio of radiocarbon to stable carbon in the plant is virtually the same as that in the atmosphere.The SUERC results showed a 95% probability that the bone samples dated from around AD1430-1460, and over in Oxford the results both came out at around AD1412-1449, again with a 95% confidence. Radiocarbon dating of marine organisms can be out by up to several hundred years, and this effect can occur to a lesser degree in terrestrial life where sea-food forms part of the diet.The mass spectrometry of the Greyfriars bone samples reveals that the individual in question had a high-protein diet including a significant proportion of seafood.
The dating process is always designed to try to extract the carbon from a sample which is most representative of the original organism.
Radiocarbon dating rests heavily on this assumption such that other sources of carbon 14 had, at first, not been considered nor accounted for.
Nowadays, radiocarbon scientists had to perform calibration not only to convert their radiocarbon year results into calendar year but also to take into account the various factors that have major effects on the global levels of carbon 14, one of which is nuclear weapons testing.
Radiocarbon’s entry into the global carbon cycle starts in the atmosphere where it is formed by the interaction of neutrons produced by cosmic rays with nitrogen atoms.
The carbon 14 produced reacts with oxygen atoms in the atmosphere to form carbon dioxide.